Page 1 of 1

Using Mlife for a lifetime fatigue estimation

Posted: Thu Jun 18, 2020 10:11 am
by Julius.Scherf
Hi everyone,

I want to use MLife to determine the fatigue lifetime for the 5MW NREL
turbine.
So far, I have run test 18 without problems. After reading up in the forum,
I've to download MLife to do fatigue estimations, but I can't find the
corresponding link.
Can somebody help me?

Thanks and best wishes,
Julius

Re: Using Mlife for a lifetime fatigue estimation

Posted: Thu Jun 18, 2020 11:47 am
by Jason.Jonkman
Dear Julius,

A similar question was asked and answered in my post dated Jun 17, 2020 in the following forum topic: viewtopic.php?f=4&t=805&start=30.

Best regards,

Re: Using Mlife for a lifetime fatigue estimation

Posted: Thu Jun 18, 2020 1:25 pm
by Julius.Scherf
Thank you for your quick reply. That helps a lot.

Best wishes,
Julius

Re: Using Mlife for a lifetime fatigue estimation

Posted: Fri Jul 03, 2020 5:54 am
by Julius.Scherf
Hi Jason,

I managed to run the mlife_certification_test file provided by mlife.
Now I want to adjust the input files in such a manner that I can determine the lifetime of the 5MW NREL turbine for all three cases specified in the IEC-61400 standard.
1. To do so, do I have to modify the DLC data files, or do I have to import the data files from FAST?
2. I'm wondering how I can plot the corresponding Wöhler curve?

Best wishes,
Julius Scherf

Re: Using Mlife for a lifetime fatigue estimation

Posted: Fri Jul 03, 2020 8:58 am
by Jason.Jonkman
Hi Julius,

I'm not sure what you mean by "DLC data files". Are you referring to the FAST time-series output files?

MLife will not plot the S-N curve for you, but you can plot it yourself using the values of L_Ult, L_MF, and m using equation (2) from the MLife Theory Manual: https://drive.google.com/file/d/1d7uWya ... sp=sharing.

Best regards,

Re: Using Mlife for a lifetime fatigue estimation

Posted: Mon Jul 06, 2020 4:12 am
by Julius.Scherf
Hi Jason,

thank you for your quick reply.
The Problem concerning the DLC files solved itself.
But regarding the S-N curve, I have a question. I understand that I can calculate the number of cycles using equation (2) with L_Ult and L_MF provided by MLife, but I'm not sure about L_i^RF. Can I understand it as such that it represents the standard deviation from each load case?


Best wishes,
Julius Scherf

Re: Using Mlife for a lifetime fatigue estimation

Posted: Mon Jul 06, 2020 6:56 am
by Jason.Jonkman
Dear Julius,

L^RF_i is the cycles load range about a fixed mean value. The S-N curve is a plot of L^RF_i (S) versus N_i (N).

Best regards,

Re: Using Mlife for a lifetime fatigue estimation

Posted: Tue Jul 07, 2020 3:12 pm
by Julius.Scherf
Dear Jason,

thank you. I appreciate your effort.

Best wishes,
Julius

Re: Using Mlife for a lifetime fatigue estimation

Posted: Fri Jul 17, 2020 11:02 am
by Julius.Scherf
Dear Jason,

I set the Weibull-Shape factor to 2, so I can assume a Rayleigh wind distribution. Further, I want to determine the lifetime damage for three different mean wind speed values (7.5; 8.5; 10 m/s). The strange thing that I observe is that the ultimate load decreases from 8.5 to 10 m/s. Is there a fundamental error I don't see. Do you have any ideas?


Best wishes,
Julius

Re: Using Mlife for a lifetime fatigue estimation

Posted: Fri Jul 17, 2020 11:10 am
by Julius.Scherf
Dear Jason,

I'm sorry, I forget to tell you that the ultimate load for the lifetime damage was calculated for RootMMxy1, which was determined as described in the MLife manual.


Best wishes,
Julius

Re: Using Mlife for a lifetime fatigue estimation

Posted: Mon Jul 20, 2020 7:02 am
by Jason.Jonkman
Dear Julius,

I'm sorry, but I'm not sure I understand. How are you arriving at the ultimate load for RootMMxy1?

Best regards,